A hairshirt worn commonly be medieval monks designed to irritate the skin and shelter lice. They were worn to cause the wearer suffering as penance for sins and to imitate the sufferings of Christ on the cross.

A barbed metal belt worn round the thigh of followers of Opus Dei, a Catholic sect. Used to recreate and remind them of the suffering of Christ at the crucifiction, and as punishment for 'sins of the flesh'.
Opus Dei missionaries have to wear it for at least 2 hours per day, except on the Sabbath and other holy days. - Pronounced 'SILL-iss'